base

Examples of base in the following topics:

• Important Reagent Bases

  • Most base reagents are alkoxide salts, amines or amide salts.
  • Since alcohols are much stronger acids than amines, their conjugate bases are weaker than amide bases, and fill the gap in base strength between amines and amide salts.
  • Hünig's base is relatively non-nucleophilic (due to steric hindrance), and like DBU is often used as the base in E2 elimination reactions conducted in non-polar solvents.
  • Barton's base is a strong, poorly-nucleophilic, neutral base that serves in cases where electrophilic substitution of DBU or other amine bases is a problem.
  • Finally, the two amide bases see widespread use in generating enolate bases from carbonyl compounds and other weak carbon acids.

• Weak Bases

  • A weak base is a chemical base that does not ionize fully in an aqueous solution.
  • As Brønsted-Lowry bases are proton acceptors, a weak base may also be defined as a chemical base with incomplete protonation.
  • A general formula for base behavior is as follows:
  • This results in a relatively low pH compared to that of strong bases.
  • The pH of bases in aqueous solution ranges from greater than 7 (the pH of pure water) to 14 (though some bases have pH values greater than 14).

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• Lewis Acid and Base Molecules

  • Lewis bases are electron-pair donors, whereas Lewis acids are electron-pair acceptors.
  • A Lewis base, therefore, is any species that donates a pair of electrons to a Lewis acid.
  • By treating acid-base reactions in terms of electron pairs instead of specific substances, the Lewis definition can apply to reactions that do not fall under other definitions of acid-base reactions.
  • Nearly all reactions in organic chemistry can be considered Lewis acid-base processes.
  • This lesson continues to describe acids and bases according to their definition.

• The Brønsted-Lowry Definition of Acids and Bases

  • Originally, acids and bases were defined by Svante Arrhenius.
  • Keep in mind that acids and bases must always react in pairs.
  • Therefore, according to the Brønsted-Lowry definition, an acid-base reaction is one in which a conjugate base and a conjugate acid are formed (note how this is different from the Arrhenius definition of an acid-base reaction, which is limited to the reaction of H+ with OH- to produce water).
  • Here, ammonia is the Brønsted-Lowry base.
  • Chemistry 12.1 What are Acids and Bases?

• Strong Bases

  • As discussed in the previous concepts on bases, a base is a substance that can: donate hydroxide ions in solution (Arrhenius definition); accept H+ ions (protons) (Bronsted-Lowry definition); or donate a pair of valence electrons (Lewis definition).
  • Strong bases are capable of deprotonating weak acids; very strong bases can deprotonate very weakly acidic C–H groups in the absence of water.
  • Generally, the alkali metal bases are stronger than the alkaline earth metal bases, which are less soluble.
  • When writing out the dissociation equation of a strong base, assume that the reverse reaction does not occur, because the conjugate acid of a strong base is very weak.
  • Unlike weak bases, which exist in equilibrium with their conjugate acids, the strong base reacts completely with water, and none of the original anion remains after the base is added to solution.

• Changing Logarithmic Bases

  • A logarithm written in one base can be converted to an equal quantity written in a different base.
  • Most common scientific calculators have a key for computing logarithms with base $10$, but do not have keys for other bases.
  • Fortunately, there is a change of base formula that can help.
  • The change-of-base formula can be applied to it:
  • Use the change of base formula to convert logarithms to different bases

• Acid-Base Titrations

  • Acid-base titration can determine the concentrations of unknown acid or base solutions.
  • An acid-base titration is an experimental procedure used to determined the unknown concentration of an acid or base by precisely neutralizing it with an acid or base of known concentration.
  • Acid-base titrations can also be used to quantify the purity of chemicals.
  • strong acid-weak base titration: methyl orange indicator the base is off the scale (e.g., pH > 13.5) and the acid has pH > 5.5: alizarine yellow indicator
  • A weak acid will react with a strong base to form a basic (pH > 7) solution.

• Changes in the Monetary Base

  • If the Fed's balance sheet changes, subsequently, both the monetary base and money supply change.
  • Next, we substitute the monetary base formula into Equation 3 because the monetary base equals deposits held by depository institutions plus currency in circulation, or B = D + C.
  • After substituting the monetary base into Equation 3, we yield Equation 4.
  • Total Liabilities = Monetary base (B) + U.S.
  • Equation 6 shows how a change in the Fed's balance sheet affects the monetary base.